Differential phase shifters conventionally used in waveguides comprise toroidal ferrite bodies whose central bores contain wiring for the generation of an axial magnetic field which controls the extent of the phase shift introduced thereby; the magnitude of this phase shift depends on the direction of the electromagnetic wave propagating through the guide and is also a function of the length of the body, as is the attenuation caused by that body. This attenuation remains substantially constant until the magnetic field generated in the ferrite attains a critical level, increasing rapidly beyond that point.
The latter property has heretofore prevented the use of such phase shifters in guide structures for high-power microwaves, such as circulators or tuners for power magnetrons.
In order to dissipate the heat generated by the transfer of electromagnetic energy to the ferrite body, dielectric inserts of good thermal conductivity are generally disposed alongside that body. The presence of this dielectric material, together with the dielectric property of the ferrite, increases the equivalent width of the guide and thus favors the propagation of higher modes therethrough. The suppression of these higher modes requires the provision of absorptive masses along the sidewalls of the waveguide.